The transformation of amorphous basic copper carbonate precipitates into the crystalline form in aqueous solutions was experimentally studied. The unique blue-to-green color change and drastic volume reduction of the precipitates in transition made continuous observation and quantitative determination of the transformation process feasible. The transformation, which involves both nucleation and crystal growth proliferation, was autocatalytic. Experimental results are in good agreement with the rate equation formulated on the two-stage kinetics model postulated for the system. Also studied were the effects of temperature and precipitate concentration on the rate of transformation. In the temperature range between 34° and 39°C., the apparent nucleation activation energy was 19.8 kcal./g.-mole.